9-2 The Krebs Cycle and Electron Transport Slide 1 of 37

Transcription

1 1 of 37

2 9-2 The Krebs Cycle and Oxygen is required for the final steps of cellular respiration. Because the pathways of cellular respiration require oxygen, they are aerobic. 2 of 37

3 The Krebs Cycle The Krebs Cycle In the presence of oxygen, pyruvic acid produced in glycolysis passes to the second stage of cellular respiration, the Krebs cycle. 3 of 37

4 The Krebs Cycle What happens during the Krebs cycle? 4 of 37

5 The Krebs Cycle During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions. 5 of 37

6 The Krebs Cycle The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion. 6 of 37

7 The Krebs Cycle One carbon molecule is removed, forming CO 2, and electrons are removed, changing NAD + to NADH. 7 of 37

8 The Krebs Cycle Coenzyme A joins the 2-carbon molecule, forming acetyl-coa. 8 of 37

9 The Krebs Cycle Acetyl-CoA then adds the 2-carbon acetyl group to a 4- carbon compound, forming citric acid. Citric acid 9 of 37

10 The Krebs Cycle Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound. 10 of 37

11 The Krebs Cycle Two more molecules of CO 2 are released and electrons join NAD + and FAD, forming NADH and FADH of 37

12 The Krebs Cycle In addition, one molecule of ATP is generated. 12 of 37

13 The Krebs Cycle The energy tally from 1 molecule of pyruvic acid is 4 NADH 1 FADH 2 1 ATP 13 of 37

14 The Krebs Cycle What does the cell do with all those high-energy electrons in carriers like NADH? In the presence of oxygen, those high-energy electrons can be used to generate huge amounts of ATP. 14 of 37

15 How are high-energy electrons used by the electron transport chain? 15 of 37

16 The electron transport chain uses the highenergy electrons from the Krebs cycle to convert ADP into ATP. 16 of 37

17 High-energy electrons from NADH and FADH 2 are passed along the electron transport chain from one carrier protein to the next. 17 of 37

18 At the end of the chain, an enzyme combines these electrons with hydrogen ions and oxygen to form water. 18 of 37

19 As the final electron acceptor of the electron transport chain, oxygen gets rid of the low-energy electrons and hydrogen ions. 19 of 37

20 When 2 high-energy electrons move down the electron transport chain, their energy is used to move hydrogen ions (H + ) across the membrane. 20 of 37

21 During electron transport, H + ions build up in the intermembrane space, so it is positively charged. 21 of 37

22 The other side of the membrane, from which those H + ions are taken, is now negatively charged. 22 of 37

23 The inner membranes of the mitochondria contain protein spheres called ATP synthases. ATP synthase 23 of 37

24 As H + ions escape through channels into these proteins, the ATP synthase spins. Channel ATP synthase 24 of 37

25 As it rotates, the enzyme grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP. Channel ATP synthase ATP 25 of 37

26 On average, each pair of high-energy electrons that moves down the electron transport chain provides enough energy to produce three molecules of ATP from ADP. 26 of 37

27 The Totals The Totals Glycolysis produces just 2 ATP molecules per molecule of glucose. The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP. 27 of 37

28 The Totals 28 of 37

29 Comparing Photosynthesis and Cellular Respiration Comparing Photosynthesis and Cellular Respiration The energy flows in photosynthesis and cellular respiration take place in opposite directions. 29 of 37

30 Comparing Photosynthesis and Cellular Respiration On a global level, photosynthesis and cellular respiration are also opposites. Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food. 30 of 37

31 9-2 Continue to: - or - Click to Launch: 31 of 37

32 9-2 The Krebs cycle breaks pyruvic acid down into a. oxygen. b. NADH. c. carbon dioxide. d. alcohol. 32 of 37

33 9-2 What role does the Krebs cycle play in the cell? a. It breaks down glucose and releases its stored energy. b. It releases energy from molecules formed during glycolysis. c. It combines carbon dioxide and water into high-energy molecules. d. It breaks down ATP and NADH, releasing stored energy. 33 of 37

34 9-2 In eukaryotes, the electron transport chain is located in the a. cell membrane. b. inner mitochondrial membrane. c. cytoplasm. d. outer mitochondrial membrane. 34 of 37

35 9-2 To generate energy over long periods, the body must use a. stored ATP. b. lactic acid fermentation. c. cellular respiration. d. glycolysis. 35 of 37

36 9-2 Which statement correctly describes photosynthesis and cellular respiration? a. Photosynthesis releases energy, while cellular respiration stores energy. b. Photosynthesis and cellular respiration use the same raw materials. c. Cellular respiration releases energy, while photosynthesis stores energy. d. Cellular respiration and photosynthesis produce the same products. 36 of 37

37 END OF SECTION